Various wireless powering methods for implantable electronics are based on nearfield or farfield coupling. These and other methods suffer from several disadvantages. A power harvesting structure in an implanted device is typically large (e.g., typically on the order of a centimeter or larger). In nearfield communications, coils external to the body can similarly be large, bulky and oftentimes inflexible. Such constraints present difficulties regarding incorporation of an external device into a patient's daily life. Furthermore, the intrinsic exponential decay of nearfield signals limits miniaturization of an implanted device beyond superficial depths, for example, at depths greater than 1 cm. On the other hand, the radiative nature of farfield signals can limit energy transfer efficiency.
Wireless midfield technology can be used to provide signals from an external source to an implanted sensor or therapy-delivery device. Midfield-based devices can have various advantages over conventional nearfield or farfield devices. For example, a midfield device may not require a relatively large implanted pulse generator and one or more leads that electrically connect the pulse generator to stimulation electrodes. A midfield device can have a relative small receiver antenna and can therefore provide a simpler implant procedure, which can lead to a lower cost and a lower risk of infection or other complications related to implant or explant.
Another advantage of using midfield powering technology includes a battery or power source that can be provided externally to a patient, and thus the low power consumption and high efficiency circuit requirements of battery-powered implantable devices can be relaxed. Another advantage of using midfield powering technology can include an implanted device that can be physically smaller than a battery-powered device. Thus, midfield powering technology can help enable better patient tolerance and comfort along with potentially lower manufacturing and implantation costs.
There is a current unmet need that includes communicating power and/or data using midfield transmitters and receivers, such as to communicate power and/or data from an external midfield transmitter to or from an implanted device, such as a neural stimulation device or a sensor device.